Consistent social structure and optimal clique size revealed by social network analysis of feral goats, Capra hircus

Social network analysis has become a valuable tool for the measurement of social bonds and can give insight into the level of social complexity in a species. However, most studies have focused on a single social group or community, and we have a rather limited understanding of the extent to which a speciesʹ network structure varies across groups and across habitats. We investigated the strength and structure of social bonds in feral goat groups in two geographical locations that differ in ecological and climatic conditions. We found that a range of strengths of social bonds existed between female goats, with behavioural and spatial measures being highly correlated. Levels of aggression between spatially proximate individuals reflected the intrinsic costs of social living, but lower rates between more strongly bonded individuals indicated a degree of social tolerance. We found a consistent social structure despite differences in demography and ecology and we propose that associations are driven by social benefits as well as by ecological requirements. We suggest that a clique size of 12–13 individuals may be optimal for goats; beyond this threshold, the system may be less stable and susceptible to fission.